Standard deadbolt door locks are designed to project a single sliding bolt into a socket of a casing of a door. This single sliding bolt construction provides only limited security for doors and windows since there is locking only at one location.
Locking mechanisms have been proposed which have multiple deadbolt locking capabilities for added security. U.S. Pat. No. 1,513,835 discloses a locking device for windows that has a pair of locking bolts movable at fight angles to each other. The mechanism of this patent, however, transmits motion from one locking bolt to the other.
U.S. Pat. No. 2,125,227 discloses a locking device for a door which projects a sliding bolt into the side casing of a door and also projects a pair of pins upwardly and downwardly into the lintel and sill of a door. The pins are not independently held in place once being locked.
Although prior multiple locking mechanisms exist, such mechanisms have many of the same failings that single locking mechanisms have. Single deadbolt locks may be forcibly unlocked by forcing the deadbolt back into its chamber with a crow bar or similar object. Prior multiple deadbolt locking devices are constructed where each deadbolt is always in an interlocking engagement with another deadbolt so whenever there is motion by one deadbolt, an equivalent motion is transferred to the other deadbolt. This transferring of motion is present even when one deadbolt is forced back into its chamber or unlocked position. By forcibly unlocking one deadbolt, the other interlocking deadbolt becomes unlocked as well.
To fully take advantage of a multiple deadbolt locking device, there is a need for a dual locking device that has deadbolts which may be maintained in a locked position independently, regardless of whether one of the deadbolts becomes forcibly unlocked.